Nah, this is complete rubbish. Creepypasta is exactly what it sounds like; An easily copy-and-pasteable story written to be creepy. This one in particular has been around for ages in some form, and without fail, every single one I've seen incorporates this little chunk (with a few alterations (pictures of ghosts rather than Unowns etc.)) :

Quote:

One video appeared in 2010 using ”special software" to analyze the audio of Lavender Town's music. When played, the software created images of the Unown near the end of the audio.

The "special software" mentioned is known as a spectral analyzer. Put simply, it creates a graph of any piece of audio, with x being time and y being the frequency (Hertz). This is what a typical spectral graph looks like:

Spoiler:

You can see that this particular piece of audio goes for >5 minutes, with the frequencies extending up above 20kHz (which suggests that there are some artifacts in the file; a correctly-mastered track shouldn't go above 19kHz usually).
If there were really "images of the Unown/ghosts" in Lavender Town's spectrum, it would sound absolutely terrible and not like music at all (not to mention the fact that the Game Boy literally didn't have the technology to accomplish something like that).

So, this particular part of the pasta is debunked, which throws the rest of it into doubt.